1. Field of the Invention
The present invention relates to a circuit board on which electrothermal converting elements having a heating resistor layer are formed, a liquid discharge head, and a method of manufacturing the circuit board. In particular, the present invention relates to a method of manufacturing a circuit board used for a liquid discharge head which converts electric energy to thermal energy and discharges a liquid by the thermal energy.
2. Related Background Art
An ink jet recording apparatus records a high definition image by discharging fine droplets of ink from discharge ports to a recording target member. At this time, the ink jet recording apparatus converts electric energy to thermal energy. The thermal energy generates air bubbles in the ink. The action forces of the air bubbles discharge liquid droplets from the discharge ports provided to a leading end portion of a liquid discharge head. The liquid droplets discharged from the discharge ports are attached onto the recording target member to record the image. In general, such a liquid discharge head has a circuit board on which plural electrothermal converting elements that convert electric energy to thermal energy are provided.
A heating resistor is a thermal converting member which converts electric energy to thermal energy.
FIG. 5 is a plan view showing electrothermal converting elements on a conventional circuit board used for a liquid discharge head. Referring to FIG. 5, plural electrothermal converting elements 20 are arranged on a substrate 11 on which a silicon oxide film has been formed as an insulating film.
In order to form each of the electrothermal converting elements 20, an electrode wiring 13 is formed and then a heating resistor film 14 is formed so as to cover the electrode wiring 13.
FIGS. 6A to 6E are sectional views taken along a line 6-6 of FIG. 5 for explaining a method of manufacturing the conventional circuit board used for the liquid discharge head. FIGS. 7A to 7E are plan views for explaining the method of manufacturing the conventional circuit board.
With reference to the drawings, the method of manufacturing the conventional circuit board will be described.
First, a silicon wafer is used as the substrate 11, and an oxide layer 12 is formed on the silicon wafer by thermal oxidation. Then, a conductive layer for forming the electrode wiring 13 is formed on the oxide layer 12 (see FIGS. 6A and 7A). Al, Al—Si, Al—Cu, Al—Si—Cu, or the like is used for the conductive layer.
Using a mask, a part which composes a heating portion 17 is formed by dry etching (see FIGS. 6B and 7B). Next, the heating resistor film 14 for forming the electrothermal converting element is formed by a sputtering method (see FIGS. 6C and 7C).
TaN, HfB2, TaSiN, or the like is used for the heating resistor film 14.
Next, using a mask, while the heating portion 17 is being formed, the heating resistor film 14 is patterned by dry etching so as to cover the electrode wiring 13 (see FIGS. 6D and 7D).
Then, a protective film 15 made of P—SiN (SiN formed by a plasma chemical vapor deposition (CVD) method) is formed. After that, a cavitation resistance film 16 made of Ta is formed on the protective film 15 by a sputtering method (see FIGS. 6E and 7E).
The circuit board used for a liquid discharge head and having the structure described above is disclosed in JP 09-011468 A.
In recent ink jet recording apparatuses, it is necessary to further narrow a space between adjacent electrothermal converting elements to achieve a higher density arrangement, thus providing higher resolution images. It is also necessary to suppress power consumption by generating air bubbles with a small amount of applied energy.
However, when the conventional manufacturing method of the circuit board described above is used, as shown in FIG. 5, the heating resistor film 14 is formed so as to cover the electrode wiring 13. Thus, a heating resistor film space 18 is unnecessarily formed. The heating resistor film space 18 serves as an alignment margin. The alignment margin would not be required if there were no misalignment between the layers, but actual manufacturing processing involves a misalignment generated between the layers, thereby requiring the alignment margin.
The heating resistor film space 18 required due to the misalignment between the layers is a big problem under the circumstances in which the heating converting elements are arranged in higher density for providing the higher resolution images.
In addition, when there is a misalignment between the layers as shown in FIG. 8B, there is a difference in area of the effective electrothermal converting element, compared with an acceptable circuit board of FIG. 8A. This causes a problem in that a current concentration portion 21 is formed in a part of the electrothermal converting element to reduce the endurance of the electrothermal converting element.
Further, when the conventional manufacturing method of the circuit board described above is employed to form an electrothermal converting element according to another form as shown in FIG. 9, the heating resistor film space 18 makes a heating space 19 Larger. Thus, bubbling efficiency is reduced and applied energy is increased.